FAQ - How are file sizes determined on Connect:Direct Tandem when no Extents are set in the SYSOPTS? (SCI52912)

Technote (FAQ)

Question

FAQ - How are file sizes determined on Connect:Direct Tandem when no Extents are set in the SYSOPTS? (SCI52912)

Answer

Historical Number

PRI30635

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It depends on which platform is receiving.

The sending platform provides current allocation based on the sending file attributes - number of blocks, extents, block size, etc.

The receiving platform does its best to interpret the size attributes provided by the sender, then calculates the space required on the local node. There's a bit of approximation involved, since differing platforms store data in different ways, with varying amounts of overhead required for the file. A Windows data set takes up only the space need to store the data (the EOF value), plus the slack space in the last disk cluster allocated for the file. The same data stored on the Tandem, in a structured file, could take up to twice that same amount of space if the "worst case" condition occurs, in which the logical records are stored one record per block with 49% slack space. For instance, a 2050 byte LRECL in a 4096 byte block. There's only room for one logical record in the block, so nearly half the space is wasted.